Chitosan is a naturally-occurring polysaccharide, and industrially, it is produced by deacetylating chitin isolated from crustaceans such as shrimps, lobsters or crabs. Chitosan is equipped with functions such as film-forming properties, antimicrobial activities, water retention properties and flocculating ability, and therefore, have been put in practical use as a functional polymer in various fields. In recent years, its applications are actively under way especially as a safe functionalizing agent capable of imparting these functions to various substrates. For example, Patent Document 1 discloses a water-based substrate treatment composition containing chitosan or the like and a metal compound. Chitosan is also widely used as antimicrobiality-imparting coating formulations for various films, nonwoven fabrics and fiber products. One of technologies desired for these coating formulations is concerned with solutions of chitosan or derivatives thereof in solvents other than water.    Patent Document 1: JP-A-2003-201576